It is proposed to study the biological properties of the naturally occurring C27 bile alcohols hydroxylated at C-25 and of their synthetic 24-nor-analogs, hydroxylated at C-25. Emphasis will be placed on their intestinal absorption, their effect on those intestinal bacteria which dehydrogenate and dehydroxylate bile acids, on cholesterol balance and on the rate-limiting enzymes of cholesterol and bile acid biosynthesis. It is further proposed to study the mechanism of the hypocholesterolemic effect of the antifungal polyene macrolide antibiotic, candicidin. This compound is probably poorly absorbed from the intestinal tract, yet lowers tissue cholesterol concentrations and induces prostatic hypoplasia. It is further proposed to synthesize analogues of the cholelitholytic agent, chenodeoxycholic acid, with a view to developing compounds which are resistant to bacterial 7alpha-dehydroxylation yet retain their ability to reduce biliary cholesterol concentrations.